themes: convert theme copying to a golang module

Change-Id: I0a1e4b79109cf9db93acb0575200f4ec8f72d3a2
diff --git a/minuitwrp/Android.bp b/minuitwrp/Android.bp
index ad66477..8005e02 100644
--- a/minuitwrp/Android.bp
+++ b/minuitwrp/Android.bp
@@ -7,7 +7,8 @@
         "soong-cc"
     ],
     srcs: [
-        "libminuitwrp_defaults.go"
+        "libminuitwrp_defaults.go",
+        "../soong/makevars.go"
     ],
     pluginFor: ["soong_build"]
 }